The invention relates to a microwave filter of the resonant cavity type having a conductive wall in which a resonant element of dielectric material is positioned. The invention also relates to a microwave filter including, more particularly said resonator.
As is known, and in particular as is stated in the preamble of French patent 2 734 084, such microwave resonators have the characteristic of being excitable only over a narrow frequency band extending about a resonant frequency. They are conventionally implemented to make microwave filters organized around one or more such resonators connected in series. As mentioned in that patent 2 734 084, previous microwave filters are of a design that makes them difficult to produce. Furthermore, heat exchange between the resonator elements and the cavities in which said elements are placed turns out to be insufficient, particularly due to the presence of members made of thermally insulating material for holding the resonator elements in position. Various resonator elements are thus proposed in the above-mentioned patent in order to resolve the problems mentioned above. One of the variants described provides for implementing a resonator element that is thin and flat, and that is positioned in a resonant cavity having a conductive wall. The element is made of a dielectric material that is at least approximately in the form of a parallelogram, and it is dimensioned and mounted in such a manner that the vertices of the parallelogram are short-circuited to one another by the conductive wall, either conductively, or else only for microwaves. Nevertheless, the resonator obtained in that variant has the drawbacks of not recovering enough of the energy which is supplied thereto and of being relatively difficult to adjust.
The present invention thus provides a microwave resonator, in particular for a filter, the resonator comprising a resonant cavity with a conductive wall in which there are positioned a plane resonator element, frequency tuning means, and intermode coupling means, the plane resonator element being made of a dielectric material in a shape that is at least approximately a parallelogram and that is disposed transversely in the cavity in such a manner that the vertices of the parallelogram that it forms are short-circuited to one another by the conductive wall, at least at microwave frequencies.
According to a characteristic of the invention, said resonator has at least one other plane resonator element, made of a dielectric material in a shape that is at least approximately a parallelogram, the resonator elements being close together, mutually parallel, and extending transversely to a central axis of the cavity, together with frequency tuning means and intermode coupling means positioned between the parallel resonator elements. This causes the resonator to have a broader working band.
The invention also provides a microwave filter which comprises at least one microwave resonator as defined above, associated with means for injecting microwave energy to the inlet of the filter to excite the resonator(s), and means for extracting resonant energy from the outlet of the filter, together with means for providing coupling between the resonators in series when the filter has more than one resonator.